On a good day it takes a signal (like from a powerful radio) roughly 3.09 minutes to go one way between Earth and Mars. So you’d say, “Hey, Charlie, how’s it going?” and over 6 minutes later you’d hear the reply, since the message can’t go faster than the speed of light.
On a bad day it can take light and radio over 22 and a half light minutes to travel one way between the two planets (45 minutes for the reply). On average Mars is 12.72 light minutes away, but it changes day to day, as you can see from the animation below.
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There are even days on Mars when Earth is behind the Sun and no signal is available at all.
This is because Mars is orbiting the Sun slower than Earth, so sometimes it’s on the same side of the Sun as Earth and sometimes it’s all the way on the other side of the Sun.
What this boils down to is that a two way conversation between Earth and Mars will not be like talking to someone on your phone here on Earth. Messages, both voice and video, will be compressed into packets and sent out. Then once the signal reaches the other planet it can be uncompressed and viewed or heard. Then a reply can be sent.
It will be sort of like how people used to write letters to each other. You write something, mail the letter, and then a few days later get a reply.
